M. Simões

Bio: M. Simões is an academic researcher from Universidade Estadual de Londrina. The author has contributed to research in topics: Liquid crystal & Biaxial nematic. The author has an hindex of 9, co-authored 35 publications receiving 209 citations.

Corresponding states of order parameter in nematic liquid crystals.

Abstract: In this work, experimental data points from which the profile of the order parameter of nematic liquid crystals can be obtained, mainly magnetic susceptibility anisotropy and dielectric anisotropy, will be used to show that when rescaled they coalesce along a common line that extends from the nematic-isotropic phase transition region, until the nematic-crystalline phase transition region. A large set of experimental data of a diversity of nematic compounds that share the presence of a nematic-isotropic and a nematic-crystalline phase transition, without another phase within, has been collected from the liquid crystals literature. Taking for each of them the temperatures of these two phase transitions as fixed points, a common temperature scale has been constructed and, in this scale, the value of each physical quantity has been uniformly fixed at the nematic-crystalline phase transition temperature. This procedure has revealed the existence of a law of corresponding states that covers the entire nematic phase. As the values assumed by these physical quantities can be used to measure the macroscopic order parameter, the use of this temperature scale suggests that it presents a common behavior that covers the entire nematic phase.

Periodic structures in a biaxial nematic phase.

Abstract: In this work experimental and theoretical results will be used to show that under convenient conditions; appropriated geometry, well chosen boundary conditions, and suitable external fields, the elastic and dynamic behavior of a sample of a biaxial nematic liquid crystal can become similar to the one observed on usual uniaxial nematic liquid crystals. It is shown that this result can be used to determine the values of some combinations of the rheologic parameters of the biaxial phase.

Global behaviour of the order parameter in nematic phase

Abstract: In this paper we study the behaviour of the order parameter of the nematic phase for all temperatures of the phase: from the neighbourhoods of the nematic crystalline phase transition region to the neighbourhoods of the nematic isotropic phase transition region To do this, we use experimental birefringence data and thermal anisotropy conductivity data in a recursive process that makes an independent and local calculation of the order parameter exponent β(T) for each temperature value T With these data, and with this procedure, we construct the profile of β(T) and reveal that it remains constant along the entire range of the phase

Corresponding states in nematic elasticity.

Abstract: A comparative study of the temperature dependence of the elastic constants of the nematic liquid crystals known as PAA (p-azoxyanisole), MBBA 4'-methoxybenzylidene-4-n-butylaniline, and 5CB (4-n-pentyl-4'-cyanobiphenyl) will be made in this work. After a regularization of their values, and with use of a unique temperature scale, the experimental data of each of these parameters will be displayed along the lines of corresponding states that are not restricted to the neighborhoods of the nematic-isotropic phase transition point, as it would be the case in a usual corresponding states law, but encompass the entire nematic phase.

Reentrant isotropic-nematic phase transition.

Abstract: This work aims at a geometrical semimicroscopic model to study the reentrant isotropic-nematic phase transition. It will be assumed that the micellar change of shape in lyotropics can be understood as the deformation of an ellipsoid which is assumed to have the idealized form of a micelle. It will be shown that such deformation is characterized by two kinds of quantities. The first one, which is a scalar determined by the ellipsoidal eccentricity, gives the intensity of the ellipsoidal deformation. The second one, which has a tensorial nature, describes the spatial distribution of such deformation and is proportional to the tensorial nematic order parameter. We construct the invariants of such deformation and couple it with the orientational order parameter to study the reentrant isotropic-nematic phase transition. We determine the thermodynamical characteristics of this phase transition and shown that it is a second-order phase transition. By comparing the theory so constructed with the experimental data, the parameters of the model will be determined.

Introduction to Phase Transitions and Critical Phenomena

Abstract: H E Stanley Oxford: University Press 1971 pp xx + 308 price ?5 In the past fifteen years or so there has been a lot of experimental and theoretical work on the nature of critical phenomena in the neighbourhood of second order phase transitions. It has not been easy to get a good overall view of this work without digging through the rather complex original literature, although there are some good review articles covering particular aspects of the work.

Spectroscopy and Dipole Moment of the Molecule C13h20beli2sesi Via Quantum Chemistry Using Ab Initio, Hartree-Fock Method in the Base Set CC-PVTZ and 6-311G** (3df, 3pd)

Abstract: The work characterizes the electric dipole moment and the infrared spectrum of the molecule C13H20BeLi2SeSi. Calculations obtained in the ab initio RHF (Restrict Hartree-Fock) method, on the set of basis used indicate that the simulated molecule C13H20BeLi2SeSi features the structure polar-apolar-polar predominant. The set of basis used that have are CC-pVTZ and 6-311G** (3df, 3pd). In the CC-pVTZ base set, the charge density in relation to 6-311G** (3df, 3pd) is 50% lower. The length of the molecule C13H20BeLi2SeSi is of 15.799A. The magnitude of the electric dipole moment |p| total obtained was p = 4.9771 Debye and p = 4.7936 Debye, perpendicular to the main axis of the molecule, for sets basis CC-pVTZ and 6-311**(3df,3pd), respectively. The infrared spectra for absorbance and transmittance and their wavenumber (cm-1) were obtained in the set of bases used. The infrared spectrum for Standard CC-pVTZ shows peaks in transmittance with Intensity (I), at wavenumber 1,125.44 cm-1, 1,940.70 cm-1, 2,094.82 cm-1, 2,178.43 cm-1, 2,613.99 cm-1 and transmittance 433.399 km/mol, 399.425 km/mol, 361.825 km/mol, 378.993 km/mol, 433.774 km/mol, respectively. While the infrared spectrum for Standard 6-311G**(3df, 3pd), shows peaks in transmittance, at wavelengths 1,114.83 cm-1, 1,936.81 cm-1, 2,081.49 cm-1, 2,163.23 cm-1, 2,595.24 cm-1 and transmittance 434.556 km/mol, 394.430 km/mol, 345.287 km/mol, 375.381 km/mol, 409.232 km/mol, respectively. It presents “fingerprint” between the intervals (680 cm-1 and 1,500 cm-1) and (3,250 cm-1 and 3,500 cm-1). The dipole moments CC-pTZV are 3.69% bigger than 6-311G** (3df, 3pd). As the bio-inorganic molecule C13H20BeLi2SeSi is the basis for a new creation of a bio-membrane, later calculations that challenge the current concepts of biomembrane should advance to such a purpose.

Calculation by Uff Method of Frequencies and Vibrational Temperatures of the Unit Cell of the Rhodochrosite Crystal

Abstract: The electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency is a crystal oscillator. Particularly one using a quartz crystal works by distorting the crystal with an electric field, when voltage is applied to an electrode near or on the crystal. Other crystals such as rhodochrosite also have piezoelectric properties. The rhodochrosite as crystal oscillator for being an alternative to those of quartz. The rhodochrosite (MnC03) shows complete solid solution with siderite (FeC03), and it may contain substantial amounts of Zn, Mg, Co, and Ca. A molecular dynamic via molecular mechanics using the UFF (Universal Forces Field) provided the vibrational frequencies of the fundamental structure of the crystal molecule. The frequencies and vibrational temperatures of the unit cell of rhodochrosite obtained by UFF were calculated in the range from 0.6059 to 1,731.38 cm-1 and 0.87 to 2,491.06 K, respectively.

Principles for manipulation of the lateral organization of aqueous-soluble surface-active molecules at the liquid crystal-aqueous interface.

Abstract: We report an investigation of the lateral organization of water-soluble, surface-active molecules within monolayers formed spontaneously at interfaces between aqueous phases and immiscible, micrometer-thick films of nematic liquid crystals (LCs; 4'-pentyl-4-cyanobiphenyl and TL205, a mixture of cyclohexanefluorinated biphenyls and fluorinated terphenyls). Using both anionic (sodium dodecyl sulfate) and cationic (dodecyltrimethylammonium bromide) surfactants, we demonstrate that the nematic order of the LCs can direct monolayers of surfactant in dynamic equilibria with bulk aqueous solutions to phase separate and assume lateral organizations at the interfaces of the LCs that are not seen in the absence of the nematic order. The lateral organization of the surfactants is readily evidenced by the patterned orientations assumed by the LCs and can be manipulated reversibly by changes in the bulk concentrations of the surfactants. Experimental observations of the effects of bulk surfactant concentration, thickness of the film of LC, nematic order, and aqueous electrolyte concentration are placed within the framework of a simple thermodynamic model. The model incorporates the dynamic equilibration of surfactant between the bulk and interface as well as the coupling between the elasticity of nematic LCs and the lateral organization of the water-soluble surfactants within the monolayers. Qualitative agreement is found between the model predictions and experimental observations, thus supporting our conclusion that LCs offer the basis of general and facile methods to direct the lateral organization of interfacial molecular assemblies.